Conventionally, as a method of lighting the main face of a light guide plate having a round shape or polygon (for example, pentagon) shape, it is known a method of providing LEDs at the entire side face of the light guide plate. For example, when a light guide plate has a main face having a round shape, as shown in FIG. 18 it is known a light device or display, wherein: a C-shaped steel having a light source having a plurality of LEDs on the inside face thereof is provided on the side face of the light guide plate; the light of the LEDs are emitted from the side face of the light guide plate; when the light enters into the light guide plate, the light diffuses by diffusion dots provided on the main face of the light guide plate. However, in this method, in which the LEDs are placed over a wide range of the side face of the light guide plate, there are problems that a great number of LEDs are required, and that large power consumption is required.
As a method of reducing the power consumption of LEDs, it can be thought of, for example, reducing the number of LEDs provided at the side face. Particularly, when the light guide plate is polygonal (for example, pentagonal), it can be thought of a method where no light source is provided in the vicinity of each curved apex while a light source is only provided at the side face of each linear side. In this case, as compared with the case where the light source is provided on the entire side face, the number of provided LEDs is reduced, which reduces the power consumption, and also as no LED is placed on the curved portion of the main face, the labor for placing LEDs can be saved. However, since no LED is placed in the vicinity of each apex, there is a problem that a region in the vicinity of each apex becomes darker than other regions, and the unevenness of brightness occurs, and the brightness of the entire main face cannot be uniform.
For such problems, for example, Patent Document 1 discloses a light device having a light guide plate, in which prisms are formed on the entire side face of the LED-provided side face of the light guide plate, and thereby light is diffused between LEDs, which allows the brightness of the entire main face to be uniform.    Patent Document 1: JP-A-2003-331628